Structural aspects of messenger RNA reading frame maintenance by the ribosome

摘要

One key question in protein biosynthesis is how the ribosome couples mRNA and tRNA movements to prevent disruption of weakcodon-anticodon interactions and loss of the translational reading frame during translocation. Here we report the complete pathof mRNA on the 70S ribosome at the atomic level (3.1-A resolution), and we show that one of the conformational rearrangementsthat occurs upon transition from initiation to elongation is a narrowing of the downstream mRNA tunnel. This rearrangementtriggers formation of a network of interactions between the mRNA downstream of the A-site codon and the elongating ribosome.Our data elucidate the mechanism by which hypermodified nucleoside 2-methylthio-N6 isopentenyl adenosine at position 37(ms~2i~6A37)in tRNA~(Phe)GAAstabilizes mRNA-tRNA interactions in all three tRNA binding sites. Another network of contacts isformed between this tRNA modification and ribosomal elements surrounding the mRNA E/P kink, resulting in the anchoring ofP-site tRNA. These data allow rationalization of how modification deficiencies of ms~2i~6A37 in tRNAs may lead to shifts of thetranslational reading frame.